1. Field of the Invention
The present invention relates to an ink set for ink jet recording, an ink jet recording method and an ink jet recording apparatus.
2. Description of the Related Art
Ink jet systems for ejecting an ink through an ink ejection port formed of a nozzle, slit or porous film have been used for many printers since a compact printer therefor is compact and inexpensive. In particular, among ink jet systems, a piezo ink jet system for ejecting an ink by taking advantage of deformation of a piezoelectric element and a thermal ink jet system for ejecting an ink by taking advantage of boiling of the ink by thermal energy are excellent in high-resolution and high-speed printing.
One currently important object of ink jet printers is high speed and high quality printing of images on a regular paper sheet. For attaining this object, Japanese Patent No. 2667401 proposes a method comprising the steps of allowing a liquid containing a cationic group-bearing compound to adhere on a recording medium, allowing the liquid to permeate into the recording medium, and forming an image by allowing an anionic dye-containing ink to adhere on the surface of the recording medium immediately after the liquid has permeated into the recording medium and disappeared from the surface thereof. However, image density may be insufficient in this method when the drying time of the ink is shortened, and long-term ejectability may be insufficient when the images are printed using a small volume of drops.
Japanese Patent Application Laid-Open (JP-A) No. 2001-294788 proposes a color ink set for attaining high speed drying, high optical density and high image quality, wherein a black ink contains water and a water-soluble solvent, the drying time of the black ink on a regular paper sheet is not more than 5 seconds, each of color inks contain colorants, water, a water-soluble solvents and a coagulant for coagulating the components in the black ink, and the permeation time of the color inks into the regular paper sheet is not more than 5 seconds. Although optical density, feathering and intercolor bleeding are excellent when pigments are used for colorants of the color inks in this method, stable long-term storability of images may not always be sufficient since the ink contains the coagulant. It has also been a problem that electrolytes and multivalent metal salts that are usually used as the coagulant have too strong of an effect as the coagulant.
JP-A Nos. 63-265681 and 2000-109735, and Japanese Patent No. 2711888 have proposed inks containing nitrogen-containing five-membered heterocyclic keto acids such as pyrrolidone carboxylic acid or salts thereof for improving ejection characteristics. The object of these methods is to improve ejectability by taking advantage of a humectant effect of the nitrogen-containing five-membered heterocyclic keto acid. However, image quality has not always been compatible with ejection characteristics when a liquid that contains the nitrogen-containing five-membered heterocyclic keto acid and the liquid that contains colorants are used together as in the present invention.
It has been impossible, in the conventional methods, to simultaneously satisfy optical density, feathering, intercolor bleeding, drying time and long-term ejectability.